GFI #273 applies only to medically important antimicrobials given in or on the feed of food-producing animals. The FDA has identified more than 100 affected drugs: List of Approved Medically Important Antimicrobial Drugs Administered in the Feed of Food-Producing Animals that Lack a Defined Duration of Use. All other dosage forms of these drugs (injectable, intramammary, tablet, etc.) already have established durations of use.

When animal drugs do not have a defined duration of use, it means the labeling on the products does not specify how long the products may be administered for an approved use. Many of the antimicrobial drugs affected by this GFI were approved decades ago. At that time, sponsors were not required to determine how long a product may be administered because antimicrobial resistance was not yet a pressing public health concern.

The FDA anticipates that sponsors of affected products should be able to have revised labeling approved that incorporates the changes discussed in this guidance within approximately three years from the publication date of this final guidance. To achieve this goal, sponsors should submit the various types of submissions for their affected applications in a timely manner as outlined in the guidance.